In the two acid solutions, the release amount reaches 73% and 50% in 6 hours, respectively. However, in 7.4 PBS, the cumulative release percentage is only about 20% in 6 hours. This is mainly due to the following reasons: the prodrug is synthesized by the proton transfer between the amlodipine and the oleic acid molecules, thus its stability in the solution is largely dependent on the pH value of the solution. As discussed in the size and size distribution section, in acidic media the amlodipine prodrug molecules will be dissociated into amlodipine molecules and oleic acid molecules, which results in faster drug release. However, the prodrug molecules are stable in the neutral pHsolution, thus the catanionic pharmacosome is stable in the solution. As a result, the release rate of amlodipine from the catanionic pharmacosome in the neutral medium is slower than that in the acidic medium.

2. Pharmacological and therapeutic properties of new derivatives of renin inhibitors and endothelin receptor antagonists, and the methods of their determination

Hypertension therapy involves the combination of rennin inhibitors with a calcium channel blocker or angiotensin II receptor antagonist. Amlodipine is one of the most commonly used calcium channel blockers in this case. Spectrophotometric, as well as chromatographic methods were used in an analysis of combined preparations for the determination of aliskiren and amlodipine. Rameshbhai et al. examined aliskiren and amlodipine in tablets after active substance extraction using methanol. Absorption spectra were registered in the range of 200–400 nm with an absorption maximum at 354.5 nm for amlodipine and 256.0 nm for aliskiren. Due to the interference of the spectra, the authors used an absorbance correction method, which allowed elimination of the mutual eﬀect of the examined substances on the results of analysis.

3. A simple and rapid method for chiral separation of amlodipine using dual chiralmobile phase additives

The calibration curve was obtained by injecting 10 μLof working standard solutions of (S)-amlodipine 3 times over the concentration range 10–500 mg mL-1 by performing a regression linear analysis of the peak area (y) of the enantiomer vs. the concentrations (x). The regression equation of the calibration curves was y = 6055x + 9223.8, with regression coeﬃcients (R2) of 0.9998 for (S)-amlodipine, and the average R.S.D. was 1.12%. The limits of detection (LOD, S/N = 3) and quantification (LOQ, S/N = 10) for (S)-amlodipine were calculated experimentally from serial dilution. Results indicated that the values of LOD and LOQ for the enantiomer were found to be 0.032 and 0.106 mgmL-1.